A human sperm is about 1/2 5 th of a millimetre long and consists of a head, a neck and a tail. The head is oval and measures approximately, 1/250th of a millimetre in diameter. It contains the chromosomes required to fertilize the ovum. The neck is a short cylindrical structure connecting the head with the tail and containing the mechanism for the movement of the tail. The tail is a thin narrow tapering structure, ten to fifteen times as long as the head. It propels the sperm forward by a rapid side to side lashing movement. The sperm travels at a speed of approximately one millimetre every ten seconds which, for its size, is comparatively fast. When it comes up against a solid object it changes direction and continues to swim until it meets a farther obstruction.
The Storage of Sperms
The formation of sperms in the testicles is a continuous process known as spermatogenesis. The life of a sperm may be as long as two or even three months. When it has been produced in the testicle it is transmitted along one of many channels until it reaches the epididymis, where it may remain for several days or even for as long as two weeks according to the degree of sexual activity. The sperms are eventually transferred from the epididymis via the vas deferens to the sac-like seminal vesicles at the base of the bladder where they are stored until ejaculation. The seminal vesicles together with the prostate secrete the seminal fluid.
Ejaculation occurs at the time of male orgasm. The ejaculation consists of rhythmic muscular contractions throughout the whole of the male genitalia during Which the seminal vesicles contract and emit the seminal fluid containing the sperms into the male urethra. Further spasmodic muscular contractions rapidly convey the fluid down the urethra to be ejaculated from the opening at the end of the penis. The average orgasm or ejaculation consists of four to ten of these forceful contractions, and during each one seminal fluid is ejaculated from the penis. The average amount ejaculated is three to five millilitres, each millilitre containing between 50 and 200 million sperms. The total number of sperms in a normal ejaculation may, therefore, vary from 150 million to 1,000 million.